PURPOSE: To restore automatically the non-response state of a terminal device by providing an automatic restoring monitor inputting a transmitted/received communication signal while being branched between an MODEM and a terminal controller.

CONSTITUTION: An MODEM signal (a) from an MODEM1 is inputted to the automatic restoration monitor 2. The automatic restoration monitor 2 monitors the monitor signal (a). The automatic restoring monitor 2 detects non-response of a terminal controller 3 and outputs an initial signal (b) to the terminal controller 3. The terminal controller 3 receives an initial signal (b), brings the state forcibly to that of power application and attains automatic restoration. The MODEM signal (a) is transmitted to the terminal controller 3.